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Author Topic: Dumb Question  (Read 3776 times)
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AG5UM
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« on: March 28, 2020, 11:24:19 AM »

I know by now, I should know how to do  this myself....but I tend to quickly overthink and complicate things,
 its the simple things that cause me the most trouble...
I need to come up with a simple basic Receiver "Mute" for my old 1940's receivers.
I have the stock DX-100 Heathkit transmitter, a couple of D-104 mic's and the old 1940's receivers.
These receivers don't have the later "mute" circuits, just a "send-receive" or "standby-receive" switch.
I have the T/R antenna relay hooked up, but not the push-to-talk,
the other day I forgot to switch the receiver and when I flipped the transmitt switch I got a nice little Squeeeel.....
no one said a thing- nice people...but very embarrassing..!!
I first thought of adding relays,etc... But, If I look through various schematics of "Mute" circuits, is there a
simple circuit I could add for the old receivers??
You would think I could handle dealing with only two switches....but I guess not.!
Anyway,
any simple , common ,old solutions??
Embarrassed.. AG5UM


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AG5UM
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« Reply #1 on: March 28, 2020, 02:57:26 PM »

I guess its tooo.. dumb of a question to get an answer...
looks like I need another pole on my T/R relay..need a "receiver muting relay", that will open
the "B-" line, where the "standby-receive" switch and the "sensitivity"- "rf-gain" control are located in the circuit.
A relay doing the same thing the switch does...
A better look at some of the old standard methods will probably be the simple answer.
T/R relay, push-to-talk, receiver mute, etc.
Keep it simple.
AG5UM
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w7fox
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« Reply #2 on: March 28, 2020, 03:21:30 PM »

If you have an RF gain control, you can disconnect the ground lead from the pot and switch it.  If you want to monitor your CW, you can add another pot across the new standby switch and that will allow you to hear your own transmission.  The old Handbooks for the early 60's have all the dope. 
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AG5UM
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« Reply #3 on: March 28, 2020, 03:29:35 PM »

While I'm in there, it would be a good time to hook-up some connections for an external S-meter.
the S-20R already has a connector on the back for a S-meter...hummmm..
Also,
If my name was Tom...
I could have claimed it was a practical joke, instead of an embarrassing mistake!
AG5UM
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AG5UM
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« Reply #4 on: March 28, 2020, 03:31:55 PM »

W7FOX,
Thanks for the response, good ideas.
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Detroit47
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« Reply #5 on: March 28, 2020, 03:41:03 PM »

Hook up a relay with the contacts in parallel wit the revive transmit switch. Wire it so when the relay is in parallel with the revive side of the switch. Leave the send receive switch in transmit.  Energize the relay with the same power source you use for your dow key. Check out most reciver schematics you will get the idea. The Super Pro 600 outlines this in the manual I believe it is the JX21 model. I am sure that someone else will elaborate. If you let me know what specific reciver you are talking about I would be more specific. I haven't got much to do but play radio and eat.

Locked down in Michigan
Johnathan N8QPC
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AG5UM
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« Reply #6 on: March 28, 2020, 04:03:54 PM »

I'm still looking up the info. suggested...good ideas.
The receiver I'm working on is the Hallicrafters S-40B, also S-20R, etc. the simple no-filters, single conversion type.
Thanks for the response.
AG5UM

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Detroit47
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« Reply #7 on: March 28, 2020, 04:45:13 PM »

There is a Photofact for the S40B on BAMA. It has a recptacle on the back of the reciver for standby.

Johnathan
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AG5UM
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« Reply #8 on: March 28, 2020, 05:23:39 PM »

My receiver does'nt have that receptacle, But I see it on the Sam's schematic you mentioned.
The S-20R does'nt have it either, but it does have the S-meter socket.
Thanks for the info. , I missed that one.
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w7fox
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« Reply #9 on: March 29, 2020, 07:36:49 PM »

I looked up the s-40B on Bama.  The sensitivity pot is as I described and can easily be brought out to an antenna relay or external switch.
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AG5UM
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« Reply #10 on: March 29, 2020, 08:11:04 PM »

Yes, I saw the connector on the Sam's schematic, Its not on the Hallicrafters schematic ,and my receivers
did'nt have that. That should be very easy to do.
Your idea of an extra pot, to use the receiver as a CW monitor is interesting.
Thanks for the responses and the lead on the Sams PhotoFact info.
Thanks,
AG5UM
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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


WWW
« Reply #11 on: March 31, 2020, 09:19:41 AM »

Or...

Assuming you use an external speaker... obviating the need to modify radios...

An extra set of contacts, or another basic relay can be used to:
A) disconnect the speaker
B) place a load across the receiver in place of the speaker

The dummy load is required so that the receiver's output transformer does not
see an "open". They don't like that much.

Alternatively, you can just set it up with two resistors as a level dropping pad
put in and out with the keying. This way the speaker continues to operate
at a lower level (you pick the level) while ur transmitting - a monitor.

Of course you can do this to a receiver with an internal speaker.

Now, with either scheme, it can be used with any receiver at all...
Muting, FYI, does nothing to "protect" the front end of the radio, so it doesn't
matter if the speaker makes sound, the RF gain is up or down, etc...

                 _-_-
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_-_- bear WB2GCR                   http://www.bearlabs.com
AG5UM
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« Reply #12 on: March 31, 2020, 09:59:26 AM »

I may have confused things by using the words "mute,muting relay",
What we were talking about is a relay to perform the same function as the "standby-recieve" or "send-receive" switch.
This removes the HV from the tubes, including the RF amp, which does protect much of the circuit,tubes,etc.
If I do want to "monitor" my sending I can simply turn the RF-gain and volume controls way down.
We are simply using a relay to put the receiver on "standby".
I think I just used the wrong wording.
73
AG5UM
Update:
My S-40B schematic shows the Standby switch does not  "remove HV", It opens the cathode on the RF amp and IF tubes,
The plate voltage is still there, I did'nt say that correctly above. I've been playing with some S-meter circuits for this radio
today, and for some reason I remembered this post.
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K9DXL
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« Reply #13 on: April 01, 2020, 07:33:12 AM »

Or...

Assuming you use an external speaker... obviating the need to modify radios...

An extra set of contacts, or another basic relay can be used to:
A) disconnect the speaker
B) place a load across the receiver in place of the speaker

The dummy load is required so that the receiver's output transformer does not
see an "open". They don't like that much.

Alternatively, you can just set it up with two resistors as a level dropping pad
put in and out with the keying. This way the speaker continues to operate
at a lower level (you pick the level) while ur transmitting - a monitor.

Of course you can do this to a receiver with an internal speaker.

Now, with either scheme, it can be used with any receiver at all...
Muting, FYI, does nothing to "protect" the front end of the radio, so it doesn't
matter if the speaker makes sound, the RF gain is up or down, etc...

                 _-_-
I took it a step further with my HQ-129X: Also routed the antenna through a set of relay contacts, so triggering the mute would simultaneously short the antenna lead to ground while disconnecting the speaker and connecting a resistor across the speaker terminals. Put this in a box, and power the relays with a wall wart transformer, and you have a muting device that will work on any receiver.
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Breathing solder fumes since 1959.  That explains a lot.
AG5UM
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« Reply #14 on: April 01, 2020, 10:12:02 AM »

If you power the relays from the wall, they are not synchronized with the transmitter.
My DX-100 has a connector on the back which brings out power for the relay, which is controlled by the transmitt switch,
and has instructions in the manual for various arrangements.
The relay then functions from either the transmitt switch or the push-to-talk...etc.
one transmitt switch, (or the push-to-talk), should be wired to accomplish all these functions at once,
Synchronized with the transmitt switch.
73's
AG5UM
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